On Wed, May 06, 2020 at 08:32:59PM -0700, sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
>
> If there are non-hotplug capable devices connected to a given
> port, then during the fatal error recovery(triggered by DPC or
> AER), after calling reset_link() function, we cannot rely on
> hotplug handler to detach and re-enumerate the device drivers
> in the affected bus. Instead, we will have to let the error
> recovery handler call report_slot_reset() for all devices in
> the bus to notify about the reset operation. Although this is
> only required for non hot-plug capable devices, doing it for
> hotplug capable devices should not affect the functionality.
Apparently this fixes a bug. Can you include a link to a problem
report? The above is a description of a *solution*, but it's hard to
understand without starting with the problem itself.
The above talks about reset_link(), which is only used in the
io_frozen case. In that case, I think the only thing this patch
changes is that when reset_link() fails, we'll return with
PCI_ERS_RESULT_DISCONNECT instead of whatever reset_link()
returned.
What this patch *does* change is that in the normal_detected case, we
previously never called reset_link() but now we will if an
.error_detected() callback requested it.
> Along with above issue, this fix also applicable to following
> issue.
>
> Commit 6d2c89441571 ("PCI/ERR: Update error status after
> reset_link()") added support to store status of reset_link()
> call. Although this fixed the error recovery issue observed if
> the initial value of error status is PCI_ERS_RESULT_DISCONNECT
> or PCI_ERS_RESULT_NO_AER_DRIVER, it also discarded the status
> result from report_frozen_detected. This can cause a failure to
> recover if _NEED_RESET is returned by report_frozen_detected and
> report_slot_reset is not invoked.
Sorry, I'm not following this explanation. IIUC this fixes a bug when
the channel is frozen and .error_detected() returns NEED_RESET.
In that case, the current code does:
* state == io_frozen
* .error_detected() returns status == NEED_RESET
* status = reset_link()
* if status != RECOVERED, we return status
* otherwise status == RECOVERED
* we do not call report_slot_reset()
* we return RECOVERED
It does seem like we *should* call the .slot_reset() callbacks, but
the only time we return recovery failure is if reset_link() failed.
I can certainly understand if drivers don't recover when we reset
their device but don't call their .slot_reset() callback. Is that
what this fixes?
After the patch,
* state == io_frozen
* .error_detected() returns status == NEED_RESET
* we set status = NEED_RESET (doesn't change anything in this case)
* we call reset_link()
* if reset_link() failed, we return DISCONNECT
* otherwise continue with status == NEED_RESET
* we *do* call report_slot_reset()
* we return whatever .slot_reset() returned
I think the change to call .slot_reset() makes sense, but that's not
at all clear from the commit log. Am I understanding the behavior
correctly?
> Such an event can be induced for testing purposes by reducing the
> Max_Payload_Size of a PCIe bridge to less than that of a device
> downstream from the bridge, and then initiating I/O through the
> device, resulting in oversize transactions. In the presence of DPC,
> this results in a containment event and attempted reset and recovery
> via pcie_do_recovery. After 6d2c89441571 report_slot_reset is not
> invoked, and the device does not recover.
Use "pcie_do_recovery()" and "report_slot_reset()" (including the
parentheses) to follow convention. Also fix other occurrences above.
> [original patch is from jay.vosburgh@xxxxxxxxxxxxx]
> [original patch link https://lore.kernel.org/linux-pci/18609.1588812972@famine/]
> Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()")
> Signed-off-by: Jay Vosburgh <jay.vosburgh@xxxxxxxxxxxxx>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> ---
> drivers/pci/pcie/err.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index 14bb8f54723e..db80e1ecb2dc 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -165,13 +165,24 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> pci_dbg(dev, "broadcast error_detected message\n");
> if (state == pci_channel_io_frozen) {
> pci_walk_bus(bus, report_frozen_detected, &status);
> - status = reset_link(dev);
> - if (status != PCI_ERS_RESULT_RECOVERED) {
> + status = PCI_ERS_RESULT_NEED_RESET;
> + } else {
> + pci_walk_bus(bus, report_normal_detected, &status);
> + }
> +
> + if (status == PCI_ERS_RESULT_NEED_RESET) {
> + if (reset_link) {
> + if (reset_link(dev) != PCI_ERS_RESULT_RECOVERED)
> + status = PCI_ERS_RESULT_DISCONNECT;
> + } else {
> + if (pci_bus_error_reset(dev))
> + status = PCI_ERS_RESULT_DISCONNECT;
As far as I can tell, there is no caller of pcie_do_recovery() where
reset_link is NULL, so this call of pci_bus_error_reset() looks like
dead code.
We did not previously check whether reset_link was NULL, and this
patch changes nothing that could result in it being NULL.
> + }
> +
> + if (status == PCI_ERS_RESULT_DISCONNECT) {
> pci_warn(dev, "link reset failed\n");
> goto failed;
> }
> - } else {
> - pci_walk_bus(bus, report_normal_detected, &status);
> }
>
> if (status == PCI_ERS_RESULT_CAN_RECOVER) {
> --
> 2.17.1
>
